Let them exercise self-determination
and bear the full cost and consequences of their choices. If there's no threat to Europe, then there's no need for us to have some 130,000 military personnel there. If there is a threat, then they should do what's necessary to meet it. That is the very essense of self-determination. As long as they have the US picking up so much of their defense burden, they're little different from the 20-something "adult" who has a job but chooses to live at home with Mommy and Daddy rather than face the real world.